This is not really calculable, nor is the number of people killed by coal calculable in any reasonable manner. However the impact of nuclear catastrophe is far far more insidious and lasting, particularly when caused by a global calamity that causes meltdown in many plants.
I suppose fear of a 9+ earthquake followed by a massive tsunami off the coast of Fukushima was considered unreasonable.
We are on a blob of rock hurtling through an unknown cosmos. Calamities are very possible. It is deeply irresponible to create projects that will make large parts of the earth uninhabitable should the power grid fail for a long period or human stewardship go on hiatus. Meteor strikes, emps, plagues, terrorist attacks, economic collapse,and other disasters are well within the realm of possibility
Because of Greenpeace's history (the death of an anti-nuclear testing activist and the destruction of one of their ships at the hands of French special forces in 1985 ), and their current anti-nuclear stance , I don't think they would back that position.
They would back the position that wind turbines are safer than coal, so you're not wrong that they might be biased to imply coal is more dangerous than it is.